Ecosystems

• 1. Define the terms "ecosystem", "community", "habitat", "population" and "species"

  Ecosystem - all the interacting living organisms and the non-living conditions in an areaCommunity - All the populations of living organisms in a particular habitatHabitat - the natural home or environment of an animal, plant or other organismPopulation - a group of organisms of the same species that live in the same place at the same time.Species - The smallest and most specific taxonomic group. Can breed to produce fertile offspring.
• Define the term "ecology"

  The study f relations of organisms to each other and their physical surroundings
• 3. Explain what is meant by the phrase "ecosystems are dynamic".


  Dynamic ecosystems are constantly changing
• 4. Define the terms "biotic factor" and "abiotic factor", and give examples of abiotic factors and biotic factors for 3 different ecosystems (a rock pool, a playing field, a large tree)


  Biotic factor - the living components of an ecosystem e.g. presence or species, population size, competition for food sourceAbiotic factor - non-living conditions of a habitat e.g. vol. of rainfall, temp. range, light intensity, wind speed
• 5. Define the term "edaphic factor" and give 3 examples.

  Edaphic factors - factors to do with soilClay - fine particles, easily waterlogged, forms clumps when wetLoam - different sized particles, retains water but does not become waterloggedSandy - coarse, well-separated particles that allow free draining, does not retain water and easily eroded
• Define the terms "food web", "food chain" and "trophic level"


  Food web - Many interconnected possible routes of energy and biomass through an ecosystemFood chain - A single possible route of energy and biomass through a food webTrophic level - Each stage in a food chain - a feeding level
• Explain what the arrows represent in a food web.

  The direction of energy flow
• Define the terms "heterotroph", "consumer", "primary consumer", "secondary consumer", "tertiary consumer", "herbivore", "carnivore" and "omnivore".

  Heterotroph - Another name for a consumerConsumer - Organisms that obtain their organic molecules and energy by feeding on other organismsPrimary consumer - Animals that eat producers in a food chainSecondary consumer - Animals that eat primary consumers in a food chainTertiary consumer - Animals that eat secondary consumers in a food chainHerbivore - Animals that eat plants - primary consumersCarnivore - Animals that eat other animals - secondary consumer or higherOmnivore - Animals that eat both plants and other animals
• Define the terms "detritivore" and "decomposer", give 2 examples of each, and explain their role in food webs

  Detritivore - animals that feed on detritus (dead and decaying material)Decomposer - An organism (bacteria or fungi) that feeds on dead organic matter, turning the organic molecules into inorganic onesDetritivores speed up decay by breaking down detritus into smaller pieces increasing the surface area for decomposers to work on. E.g. Woodlice and earthwormsDecomposers break down dead organisms releasing nutrients back into the ecosystem. E.g. microscopic fungi, bacteria, toadstools and bracket fungi
• Define the terms "biomass" and "dry mass", and explain why dry mass is a better indicator of biomass than fresh mass.

  Biomass - The mass of living material present in a particular place or in particular organismsDry mass - The mass of living material remaining once all the water has been removedDry mass is a more reliable measure of mass as it excludes fluctuating water concentrations
• Explain how to calculate the dry mass of each tropic level in a food chain

  Organisms killed and placed in oven at 80°C until water has all evaporated - 2 identical mass readings
• Explain how to experimentally measure the energy content of organic matter.

  Using calorimeter - burn matter and measure temp. rise of water
• Suggest suitable units for the biomass in an ecosystem (both terrestrial and aquatic).

  terrestrial: gm^(-2) grams per metre squaredaquatic: gm^(-3) grams per metre cubed
• Explain how pyramids of numbers, biomass and energy represent data about an ecosystem and the relative merits of each.

  Pyramid of numbers - show number of each organism in a food chain - not always pyramid shapedPyramid of biomass - shows mass at each trophic level in a food chain - almost always pyramid shapedPyramid of energy - shows energy available from each level - always pyramidNumbers - easy to count, hard to draw due to variation Biomass - easier to draw, may still be skewed due to time of year/reproduction rateEnergy - hard to calculate
• Suggest suitable units for the energy at each trophic level in a food chain and explain why these units are appropriate.

  kJm^(-2)yr^(-1) Kilojoules per metre squared per yearper year to account for fluctuations in photosynthetic production and feeding patterns
• Explain how energy is transferred from one trophic level to the next.

  Biomass and the energy contained within its carbon compounds is transferred between trophic levels as organisms feed on each other. When animals eat, only a small proportion of the food is converted into new tissue (biomass) and therefore only a small proportion of the energy is available for the next level to eat.
• Define the term "ecological efficiency" and write an equation to calculate it.

  The efficiency with which energy or biomass is transferred from one trophic level to the next.Calculated by dividing energy or biomass available after the transfer by the energy or biomass available before the transfer. Times 100 for percentage.
• Explain 3 reasons why only 1-3% of the sunlight producers receive is converted into chemical energy.

  Not all energy used for photosynthesis - 90% reflected, some transmitted through the leaf, some is an unusable wave lengthOther limiting factors for photosynthesis eg water availability Proportion of energy 'lost' as it is used for photosynthetic reactions
• Define the terms "gross production", "net production" and "respiratory losses" and write an equation to link the three terms.


  Gross production - total solar energy that plants convert to organic matterNet production - the energy converted into biomass and therefore available to the next trophic levelRespiratory losses - energy used in respiration so not available to next trophic levelNet production = Gross production - Respiratory losses
• Define the terms "primary production" and "secondary production".

  Primary production - generation of biomass in a producerSecondary production - generation of biomass in a consumer
• Explain 4 reasons why consumers at each trophic level convert only a small amount of the biomass in the trophic level below to their own organic tissue.

  Consumers convert at most 10% of food biomass to tissue because...Not all biomass is eaten e.g. plant roots, bones etc.Energy is transferred to environment as metabolic heat (result of movement and respiration)Some parts eaten but indigestible (egested as faeces)Some energy lost from animal in excretory materials such as urine
• Draw, label and annotate, a diagram showing the flow of energy through trophic levels and out of the food chain.


  Energy lost at every level as heat from respiration.All dead matter through decomposers and detritivores who also produce heat

  
• Explain why biomass decreases at each trophic level in a food chain.

  Each level receives less energy than the level before due to energy losses such as in respiration
• Explain why food chains with more than 4 trophic levels are rare.

  There is not enough energy available as biomass to sustain another tier of organisms
• Describe how humans have manipulated energy transfer through trophic levels in the farming of plants and animals to our advantage.

  Provide abiotic conditions needed to thriveRemove competition from other speciesRemove threat of predatorsMinimise trophic levels so least amount of energy is lost in transfer as possible
• Compare the movement of energy through an ecosystem with the movement of elements such as nitrogen and carbon.

  Energy moves through ecosystems in a linear way, constantly replenished at the start by the sun. There is no large external source of nutrients such as C and N so they must be recycled round the ecosystem
• Draw, label and annotate a diagram of the nitrogen cycle.


  Nitrogen fixing bacteria : Rhizobium in root nodules and Azotobacter in the soilNitrifying bacteria : Nitrosomonas from ammonia to nitrites and Nitrobacter from nitrites to nitratesDenitrification from nitrates to nitrogen is by Pseudomonas denitrificans

  
• Explain the importance of decomposers and detritivores in the recycling of matter in ecosystems

  Detritivores speed up decay process by breaking down organic material into smaller pieces for decomposers to work on. Decomposers break down the organic matter into small inorganic molecules that can then be used by producers. The organic molecules that contain the essential elements C and N cannot be used directly.
• Define the terms "nitrogen fixation", "nitrification", "denitrification", and "ammonification"

  Nitrogen fixation - conversion of nitrogen gas to ammonium compoundsNitrification - conversion of ammonium compounds into nitrites and nitratesDenitrification - conversion of nitrates into nitrogen gasAmmonification - conversion of nitrogen compounds in dead organic matter or waste into ammonium compounds by decomposers
• Name the micro-organisms involved in the nitrogen cycle and state the nitrogen-containing molecule they use and the nitrogen-containing molecule they produce.

  Nitrogen fixing bacteria (Nitrogen to ammonia) : Rhizobium in root nodules and Azotobacter in the soilNitrifying bacteria : Nitrosomonas from ammonia to nitrites and Nitrobacter from nitrites to nitratesDenitrification from nitrates to nitrogen is by Pseudomonas denitrificans
• Draw, label and annotate a diagram of the carbon cycle.

  
• Explain why carbon dioxide levels in the atmosphere may vary throughout a 24 hour period, seasonally and over many years.

  Rate of photosynthesis and therefore rate of use of carbon dioxide fluctuates with light intensity. At night carbon dioxide levels higher as respiration continues but photosynthesis doesn't. Carbon dioxide levels lower in Summer as more light so more photosynthesis.
• Suggest two reasons why carbon dioxide levels in the atmosphere have increased significantly over the last 200 years.

  Industry - increased burning of fossil fuels - more carbon dioxide releasedDeforestation - fewer large areas of trees - less photosynthesis - less carbon dioxide removed from atmosphere
• Suggest how scientists gather data about the atmospheric carbon dioxide levels and temperature thousands of years ago

  By looking at ice at poles that formed 1000s of years ago and has never melted - air bubbles trapped in ice
• Define the terms "succession", "primary succession", "secondary succession", "deflected succession", "pioneer species", "seral stage" or "sere", "climax community" and "plagioclimax".

  Succession - the progressive replacement of one dominant type of species or community by another in an ecosystem, until a stable climax community is establishedPrimary succession - occurs on an area of land that has been newly formed or exposed such as bare rock. There is no soil or organic material present to begin with.Secondary succession - this occurs on areas of land where soil is present, but it contains no plant or animal species. An example would be the bare eather that remains after a forest fire.Deflected succession - when the direction of succession is affected by farming or other human activities such as mowing, grazing, burning crops etc.Pioneer species - the first organisms to colonise an areaSeral stages/sere - the steps in successionClimax community - final stage in succession, where the community is said to be in a stable statePlagioclimax - stage in succession where artificial or natural factors prevent the natural climax community from forming
• Give 5 adaptations that some species have for being pioneer species.

  The ability to produce large quantities of seeds or spores, which are blown by the wind and deposited on the 'new land'Seeds that germinate rapidlyThe ability to photosythesise to harness own energy - light, rainfall and air often only abiotic factors presentTolerance to extreme environmentsAbility to fix nitrogen from the atmosphere, so adding to the mineral content of the soil
• Describe the effect pioneer species have on the environment.

  As they die, their organic matter makes the environment more able to support other species - creates humus for soil - nutrients etc.
• Describe how the conditions of the soil change as succession occurs (and why).

  Weathering of bare rock produces particles that form the basis of soil. organisms of pioneer species die and decompose releasing small organic products into the soil - humus
• Explain why succession occurs.

  Succession occurs as a result of changes to the environment (the abiotic factors), causing the plant and animal species to change
• Define the term "dominant species"

  The most abundant species in an ecosystem